Quantified risk assessment

In the North Sea this is often done with detailed quantified risk assessments and the calculation of an overall IRR or risk of total loss of structure. Mitigation measures are incorporated until it can be shown that risk levels meet a minimum criteria and the cost of further mitigation has such high cost to benefit ratios that further mitigation is no longer practicable. ... 

When dealing with quantified risk assessment, these definitions need to be linked to some form of numerical value for a defined effect. It is also necessary to distinguish between individual risk and societal risk when drawing conclusions. 

Baksteen H., Mud M., Papazoglou I.A., Aneziris O. N., Ale B.XM, Bellamy L.X, Hale A.R., BloemhoffA. Post J., Oh J. 2006. Quantified risk assessment for contact with a moving part of a machine. Working on Safety Conference2006, Dutch Ministry of Social Affairs and Employment and the Delft University ofTechnology, Netherlands. 

The amoimt of detail and effort required increases from quahtative (Q) approach to semi-quantitative (SQ) one to quantified risk assessment (QRA). For the Q or SQ approaches, a risk matrix is a convenient method of ranking and presenting the results. It is important that the risk matrix used should be capable of... 

The regulatory principles developed on the NCS are in line with the recommendations in the Lord Cullen report after the Piper Alpha disaster. Cullen largely abandoned any faith in the abihty of the law, even in the form of more adaptable secondary legislation. Instead, the report placed more responsibility on means as a Quantified Risk Assessment to speak to the industry in a language that it could understand and to shift the role of the regulator fiwm one of physical inspection to one of reviewing the safety management system of the operator (Paterson, 2007, p. 58). 

How successful these new risk management techniques are is the subject of a critical literature. The trend to the greater quantification of risk, for example, is hotly debated. The mathematical basis of the quantified risk assessments (QRAs) is disputed, especially where there are small numbers involved or where there are no reliable data to work from (Cohen, 1996 Toft, 1996). The interpretation of the data may prove difficult in a variety of ways. For example, the causes of a risk may not be clear, and even where they are clear the decision about what is an acceptable risk needs to be taken and that is essentially a political decision. Indeed some claim that the procedures themselves are value laden (Hood and Jones, 1996). A more extreme position negates the whole attempt to produce an objective measure of risk, arguing that all assessments are inherently subjective (Slovic, 1992). Difficulties with these measures and approaches were recognized by industry representatives and regulators alike. One of the... 

These sorts of arguments were thus taken into accoimt in the weighting system used by the industry. The HSE s Annual Safety Report 1996197 picked up these arguments. It stated that the elimination of risk was not a possibility, especially within the limits of the law (HSE, 1997 12 ff.). But it emphasized that quantified risk assessment (QRA) and cost-benefit analyses should be seen as aids to decision-making and it criticized some employers for tending to present QRAs as a precise justification for their position either for taking no action to improve safety or, worse still, as a justification for reducing the level of safety already provided (HSE, 1997, p. ix). 

The method adopted in many industries is to use a Value of Preventing a Fatality (VPF). The VPF is the amount that an organisation will spend to reduce risk by a single fatality, and is used in cost benefit analysis (CBA) to assess reasonable practicability. The costs and benefits of a potential risk control are evaluated, and if the cost per life saved is less than or roughly equal to the VPF, the risk control is regarded as reasonably practicable and must therefore be implemented. The quantitative approach was formalised by the Health and Safety Executive (HSE) in its 1988 paper (updated in 1992) The Tolerability of Risk from Nuclear Power Stations and its 1989 paper Quantified Risk Assessment its Input to Decision Making Whilst the 1988 paper was developed for the nuclear industry, its principles have been applied widely. 

Quantified Risk Assessment its Input to Decisions Making HSE 1989... 

Quantified Risk Assessment Technique Part 2 Event Tree Analysis ETA, The Institute of Engineering and Technology Health and Safety Briefing No 26h, August 2012. 

Although this guidance focuses on the LOPA technique, other techniques such as fault tree analysis or detailed quantitative risk assessment, used separately, may be a more appropriate alternative under some circumstances. Quantified methods can also be used in support of data used in a LOPA study. It is common practice with many dutyholders to use detailed quantified risk assessment where multiple outcomes need to be evaluated to characterise the risk sufficiently, where there may be serious off-site consequences, where the Societal Risk of the site is to be evaluated, or where high levels of risk reduction are required. 

LOPA is not normally used to assess Societal Risk because a Societal Risk assessment typically requires the evaluation of a range of scenarios. This is typically carried out using quantified risk assessment techniques such as fault and event trees. There is no universally agreed method of presenting the results of a Societal Risk assessment, but comnrxjnly used methods include F-N curves and risk integrals. 

Bow-tie diagrams can be used as a stand-alone qualitative hazard identification tool or as the first step in a quantified risk assessment. Depending on the software used, the data on a bow-tie diagram may be output as a hazard register and responsibilities for ensuring that barriers are effective may be assigned. 

The implications of dispersion in low wind speed conditions br quantified risk assessment CRR133 HSE Books 1997 ISBN 978 0 7176 1359 5... 

Safety aspects of front end engineering design (FEED) QRA = quantified risk assessment ALARP = as iow as reasonably practicable. 

In technical safety, risk is a function of accident frequency and accident consequences. Pure quantified risk assessment (QRA, also called probabilistic risk assessment or PRA) typically uses mortality (i.e., the number of assessed deaths in any given potential accident situation) as a measure of consequences. The overall risk for a variety of potential accidents at a particular process plant can be plotted against recognized risk criteria in a graph of accident frequency against mortality, to help make judgments about whether the plant is acceptably safe or not. 

This involves the quantified risk assessment by considering the consequences of failure (often referred to as KAZAN). 

SET MAXIMUM TOLERABLE FAILURE RATES by carrying out a quantified risk assessment based on a maximum tolerable probability of death or injury, arising from the event in question. This is dealt with in the next Chapter and takes into account how many simultaneous risks to which one is exposed in the same place, the number of fatalities and so on. 

This chapter may seem to describe a different rule-based graph-type approach to the methods encouraged throughout this book. It has to be said that the authors believe these to be not fully calibrated (i.e., dimensioned) against assessments from comparative quantified risk assessment approaches or from field failure data. 

Assume that a quantified risk assessment has predicted a probability of 20% that failure, involving overpressure, will lead to subsequent pipe rupture and ignition. Furthermore it is predicted that, due to the high population density, fatality is 50% likely. 

This chapter is in two parts. The first presents some helicopter accident and fatality statistics to provide a comparison with other activities. The second is an example of a quantified risk assessment, which required an input from the foregoing statistics. 

Safety requirements should be derived from the defence/protection measures stored in the SHL and some of these requirements will be quantified using the Quantified Risk Assessment model. A Safety Requirements Forum be formed, to assemble sufficient expertise necessary to elicit safety... 

The main shortcomings of quantified risk assessment (QRA) are cost (often the cost of this activity cannot be easily justified, particularly for simple imdertakings) and lack of reliable data (particularly if the imdertaking is about a novel and/or complex change). On the other hand, quahtative risk assessment often results in unsubstantiated arguments based aroimd informal estimates of consequence occurrence and associated loss. In addition to that, some problems are very difficult, if not impossible, to model for example, system failures related to human action and software performance, without experiential data being available. 

Health and Safety Executive (1989) Quantified Risk Assessment Its Input to Decision Making HMSO, London... 

HSE (1989) Quantified Risk Assessment Its input to decision making, HSMO London and Cox SJ and EF O Sullivan (1992) Building regulation and safety. (BRE Report), UK Construction Research Communications Ltd, Figure 4, pp 57. 

FMEA COSHH Failure Mode and Effect Analysis Control of Substances Hazardous to Health QRA Quantified Risk Assessment... 

Quantified Risk Assessment is valuable at all stages in the life of a plant All plants contain residual risk. Action to evaluate and reduce risk should continue throughout the life of a plant by seddng to eliminate the root cause of incidents particularly with re )ect to maintenance, external threats, procedures, information, information transfer and information processing, the abilities of personnel in the task, and the capabilities d management and organisation. 

Layout and spacing considerations as developed during hazard study 2. Also any special building design requirements, area classification requirements, and quantified risk assessments, overpressure circles or offsite risk analyses as appropriate. 

Incorporating human error in case for safety risk assessment For many years there has been a requirement in the nuclear industry for plants to develop a Safety Case and have it approved by regulators in order to obtain a licence to operate. The Safety Case is, essentially, a very comprehensive quantified risk assessment based on the aggregated probability of an event (for example, the escape of radiation) against a defined benchmark probability. Once the licence has been granted, the Safety Case has to be formally reviewed at defined intervals. 

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